Noted Bug. I've seen this happen repeatedly usually when I'm getting attacked, since I rarely have the Bonus Damage 2. However I can definately confirm it is not working for at least the character Fifty, as my opponent attacked me with him during a match with the bonus active and I only took 5 damage. The Fifty was lvl 2 at the time, which is when he does 5 damage normally.
I do know it works for other characters Lao for example has no problems hitting me for 10. It may just be Fifty or the Bangers team in general. More testing is needed but this is definately something I've seen happen more than once.
The Bug involving Fifty and 1 Clintz and 1 Points does not seem to be limited to him leveling up but just appearing in general
Further confirmation of Bangers 2 Damage problem. Badenpower and Vermyn N (no presence of Fifty, Fifty was removed from the Deck), also suffered the same problem. Only Fifty causes the clint/points errors. Other Bangers do not cause this Bug.